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A144848
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a(n) = number of distinct prime divisors (taken together) of numbers of the form x^2+1 for x<=10^n.
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5
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7, 70, 720, 7102, 70780, 704537, 7026559, 70122424, 700184485, 6993568566, 69870544960
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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LINKS
| B. Helmes, Quadratisches Siebverfahren/Primzahlgenerator
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MATHEMATICA
| d = 10; l = 0; p = 1; c = {}; a = {}; Do[k = p x^2 + 1; b = Divisors[k]; Do[If[PrimeQ[b[[n]]], AppendTo[a, b[[n]]]], {n, 1, Length[b]}]; If[x == d, a = Union[a]; l = Length[a]; d = 10 d; Print[l]; AppendTo[c, l]], {x, 1, 10000}]; c (*Artur Jasinski*)
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CROSSREFS
| For primes of the form n^2+1 see A002496
Cf. A002496, A143835, A143868, A144848, A144849, A144850, A144851
Sequence in context: A043034 A015251 A196662 * A180902 A078246 A097184
Adjacent sequences: A144845 A144846 A144847 * A144849 A144850 A144851
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KEYWORD
| base,nonn
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AUTHOR
| Artur Jasinski & Bernhard Helmes (bhelmes(AT)gmx.de) (grafix(AT)csl.pl), Sep 22 2008, Sep 24 2008
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